Pressure filter and process for cleaning it

ABSTRACT

In a pressure filter for liquid media a plurality of filter elements is supported by a removable hollow cross bar which, when the filter tank is opened, can be removed together with all or groups of the filter elements. The filter element has a flexible filter wall and preferably an outer fine meshed wall and an inner coarse meshed wall. 
     Between the two wall portions a packing material is arranged. Preferably the entire filter element is a flexible tube element. Spray tubes are arranged in the filter tank which are also removable together with their supporting carrier member. The spray elements serve to rinse out the filter cake. This may be done by passing the rinsing agent successively at spaced time periods through individual groups of the filter elements.

BACKGROUND OF THE INVENTION

The invention relates to a pressure filter for liquid media and inparticular a pressure filter which is equipped with flexible hose-typefilter elements.

In the prior art filters of this kind all individual elements aresupported on one carrier bar or carrier disk. After opening the lid ofthe filter tank the entire package of filter elements must be removedupwards by means of a lever device if a control and cleaning is desired.The individual elements which form part of a package of elements aredifficult to remove and usually removal is impossible without concurrentremoval of the surrounding elements. In case of a defect of a singlefilter hose element it is therefore necessary to remove an entire row offilter elements. In order to lift the entire package of elements in viewof the weight of the carrier member and the large number of elements,large dimension crane structures are necessary which must be placedabove the filter tank. Therefore, a comparatively great height is alwaysnecessary for the structures.

Filter hose elements of this kind are known from the German publishedapplications Nos. 2,114,226 and 1,917,306. The flexible filter elementsemployed there are provided with various inside support elements. Filterhose elements without supports would be compressed inwards during thefiltration. The prior art supports have resulted in an improvement ofthe filtration properties of this type of elements but they have alsomade it necessary to employ additional material and to incorporate it inthe structure and thus have caused additional expense. The object of theinvention is a filter which does not require elements for the support ofthe filters.

SUMMARY OF THE INVENTION

This object is solved by a pressure filter in which the carrier elementis provided removable upon opening of the filter tank and wherein theindividual filter elements are supported by this carrier element. Thefilter elements may be arranged in rows on a plurality of carrierelements and there may thus be removed individual groups of filterelements as desired. The filter elements themselves are provided with anexterior filter wall which may be a flexible textile and in the interiorof the element packing material is provided. There may also be a spacedinner wall and the packing material may be provided between the twowalls with the central space inside the inner wall adapted to receivethe filtrate which is passed out through the hollow carrier member orother discharge devices.

The surprising discovery of the present invention is that specialsupports as shown in the mentioned German application No. 2,114,226 areno longer necessary.

The hollow body which is used as the collecting tube and carrier forremoving individual filter segments may be freely supported on anannular disk and may be connected with the discharge tubes by a flangeand a releasable connection. The collecting tube may be provided withinor outside the filter tank. The individual removable hollow carriersegments can be of different length and may support varying numbers offilter elements which may be arranged in rows on a plurality of suchcarrier elements.

It has been found that it is highly useful to provide a baffle plate atthe lower portion of the filter tank close to the entry of the liquid tobe filtered in order to protect the filter elements when they arecovered with filter cake against excessive tubulence of the enteringslurry.

It has also been found that the filter elements preferably comprise aninner wide mesh and an outer fine mesh filter cloth. The inner cloth inthis case serves as a retaining means for the packing material. Theouter cloth primarily is the filter agent proper.

This structure also has the advantage that during backwash the innercloth is not subject to stretching.

Suitable materials for both wall portions may be plastics, naturalfibers or permeable metal.

In a special embodiment of the invention apertures may be provided inthe area where the inner cloth is supported by a connecting tube whilein the same area the outer cloth may be impermeable so that duringbackwash the rinsing current can rapidly enter between the two clothsand the filter cake can thus be removed uniformly from all parts of thefilter elements. Thus, the rinsing medium during backwash, be it aliquid or gas, is distributed by the hollow carrier element to theindividual filter elements. Groups of filter elements can thus be rinsedsuccessively in spaced time periods. This also helps to accomplish auniform removal of the filter cake.

The backwash can be effected with a vaporous rinsing fluid. The fluid inthat case is fed as a vapor or mist into the filter tank and pressedthrough the filter cake.

There exist however filter cakes which are very difficult to remove andwhich cannot be completely removed by compressed air or a backwash withliquid. For cases of this kind it is proposed to arrange between tworows of filter elements, a row of spray tubes extending throughout theentire length of the filter elements. These spray tubes are alsoprovided on a removable carrier element which may be connected by aflange or clutch to an inlet tube. The spray tubes may be provided withspray nozzles.

The filter elements according to the invention are filled with variouskinds of packing materials. For this purpose there may be used Raschigrings, Berl saddles, and further also glass balls, stones, quartz sand,coal, coke and catalysts. Raschig rings of the same diameter as theinner diameter of the filter hose can be arranged in columns on top ofeach other. The arrangement must, however, be such that at the front endthe liquid in the form of the filtrate can penetrate. Rings of metal orceramic having lateral apertures are also useful as packing materials.For special application metal catalysts, fuller's earth, activated coaland other surface active materials, preferably in the form of granulatesmay be used. The particles of the granulates may be made stationary by asuitable adhesive, for instance a synthetic resin or sodium silicate(water glass).

It is preferred to use as packing material bodies of a specific weightbelow 1. Useful are, for instance, spherical fillers of bloated claysuch as are used as structural and insulating materials under thetradename Leca-Korn which are made by Hunziker-Baustoffe corporation ofBern, Switzerland. This material is resistant almost against allchemicals and hard and non-abrasive. The weight by volume of the loosegrains in dry condition is between 330 and 700 kg/m³ ; the grain size isbetween above 0 to 20 mm diameter. It is, however, possible also to useinorganic bloated materials with an open or continuous surface andplastics in the form of hollow spheres. The individual bodies may befixed in their relative position.

If the filters are employed for catalytic reactions it is preferred toform a central hollow space in the interior of the element which can bedone for instance by inserting a type of sieve tube into the filterelement.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section through a pressure tank filter;

FIG. 2 is a section through the filter of FIG. 1 on lines A--A;

FIG. 3 is a modification of the discharge for the clear liquor in thedome of the filter tank of FIG. 1;

FIG. 4 is another embodiment of the discharge portion for the filtratein the dome of the filter tank;

FIG. 5 is a cross section through the embodiment of FIG. 4 along linesA--A;

FIG. 6 is a cross section through a filter tank which is provided with aspray tube device for rinsing purposes;

FIG. 7 is a cross section through FIG. 6 along lines A--A;

FIG. 8 is a longitudinal section through a filter element; and

FIGS. 9 to 13 are similar cross sections through other embodiments offilter elements.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference particularly to FIGS. 1 and 2 it will be seen that 1shows a filter tank which is provided with tube-like filter elements 9.In the lower portion of the tank 1 which, of course, may also haveconical form, an inlet tube 2 and an outlet tube 13 are provided, thelatter serving as the outlet for the filter residue.

The filter tank 1 and its lid 5 are connected by means of a T-shapedintermediate ring 25. The ring 25 is releasably connected to the flange14 of the tank by means of a cooperating flange 23. One half of theannular ring 25 is provided with a support ring 28 welded to its innerwall.

In the wall of the other half of the annular ring 25 bores are providedwhich communicate with connecting tubes 8 which latter extend throughthe outer wall of the tank and lead to a collector tube 6 which isprovided with a discharge opening 3. The top portion 5 is connected bymeans of a flange 15 to the upper flange 24 of the annular bridgeportion 25.

In the left-hand filter element the section shows the upper portion ofthe filter element 9 with the packing material 10.

The baffle plate 22 which is provided beneath the filter element has thepurpose to prevent excessive turbulence in the filter tank in order toprevent an unintended rinsing out of the filter cake which has formed onthe outside of the filter elements.

With reference now to FIG. 3 it will be seen that in this case the tank1 is provided with a lid which can be locked by means of the flange 14of the main tank portion and the flange 15 of the top portion. The topof the tank is also provided with an outlet 3a for the clear liquor andan exhaust opening 4. The collector tube 6a in this case is provided inthe interior of the tank and is connected by tubes 8a to the hollowcarrier member 7a for the filter elements. The filter elements 9 areattached to the hollow carrier member 7a and thereby to the collectingtube 6a by means of connecting tubes 11 which are attached to the filterelements by means of flanges or other fastening elements 12.

FIG. 4 shows another embodiment of the upper portion of the filter tank.It will be understood that the lower portion of the tank is identicalwith that shown in FIG. 1. The carrier member in this case is formed bya disk 16 which is fastened between the flange 14 of the main tankportion and the flange 15 of the lid portion. The disk-like carriermember in this case forms a separating wall between the lower portion ofthe tank in which the liquor to be filtered is received, and the upperportion which is the receptacle for the clear liquor. For this purposethe separator and collector disk 16 is provided with bores 17 of whicheach corresponds with one of the filter elements 9. The filter elementscommunicate with the hollow carrier disk by means of the connecting tube11a which is fastened to the filter elements by a fastening ring 12a ina similar manner as in FIG. 3.

An air inlet and outlet is provided in this case in the lower portion ofthe tank that is below the separating and collecting disk 16 (part 4a).The bores 17 of the carrier disk which connect with the filter elements9 and the outlet for the filtrate 3a which connects with the collectingtube 6a are more clearly shown in the section of FIG. 5.

The embodiment shown in a longitudinal section in FIG. 6 and in crosssection in FIG. 7 shows a filter tank which is provided with spray tubes30 which may be made of metal or a plastic. The tubes 30 are providedwith a multitude of spray bores 31 in which nozzles may be provided.

As is shown particularly in FIG. 6, one row of such spray tubes 30 isdisposed in the space between two rows each of filter elements 9. Thespray tubes are in communication with a distributor pipe 32 which isprovided with an inlet 35. The distributor tube is disposed above thehollow carrier member 7. After opening the top portion 5 of the tank andreleasing the flange 33 each distributor tube 32 with the connectedspray tubes 30 can be separately removed. Between the distributor tube32 and the inlet opening 35 there is provided a connecting tube 34.

The filter elements themselves are shown in different embodiments inFIGS. 8 to 13.

FIG. 8 illustrates a comparatively simple form of filter element whichis provided with a filtering agent in form of a wall 18 which mayconsist of a plastic cloth such as "Teflon", nylon, "Perlon" or naturalfibers or also fine meshed metal cloth. The width of the apertures ofthe cloth depends on the size of the solid particles which are to beremoved by the filtration. The interior of the tube-like filter element9 is filled with the packing material 10. A screen plate 19 forms abarrier to prevent penetration of the packing matter into the filtratespace of the tank by way of the connecting tube 11.

The filter cloth which forms the outer wall is provided with a seam 21to hold together its two sections and is attached at its upper end bymeans of a fastening link 12 to the connecting tube 11.

FIG. 9 shows another embodiment where the outer wall is again thefiltering agent 18 while there is provided an inner wall by way of asolid tube 20. The spring plate 19 in this case is disposed at the loweropening of the tube 20. The packing material 10 is disposed in the spacebetween the tube 20 and the filtering wall 18.

FIG. 10 shows a similar embodiment where, however, the inner tube isformed by a perforated flexible wall 20a, The packing material isdisposed in the intermediate space 21a between the inner wall 20a andthe outer filtering wall 18. The packing material, for instance may be acatalyst granulate.

FIG. 11 is a similar embodiment in which, however, the inner wall isformed by an apertured tube 20b which at its lower end is closed by ascreen plate 19.

FIGS. 12 and 13 show more distinctly the connection between the filterwalls proper and the connecting tube 11 which leads to the hollowcarrier member 7. The connection as appears is again held by a fasteningring 12. In FIG. 12, however, as distinguished from FIG. 11 the packingmaterial is provided in the innermost space inside the inner wall 20cand the outer wall formed by the main filtering agent 18. Both the outerand the inner wall consist of cloth type filter elements, the outerwall, however, having a finer mesh size than the inner wall. In thiscase the screen plate 19b is provided at the open end, (FIG. 12) of theinner wall portion or (FIG. 13) at the open end portion of both wallmembers. Thus, the penetration of the packing material into theconnecting tube 11 is prevented. The filter walls are again connected tothe connecting tube 11 by means of a fastening ring 12.

The connecting tube is provided with openings 23 and the inner wallmember in FIG. 12 and the inner wall member 20c in FIG. 12 hascorresponding openings. The same type of openings is used in theembodiment of FIG. 13 where, however, the outer wall member and theinner wall member are immediately contiguous. The length 11' of theouter wall member which laps the lower portion 11" of the connectingtube 11 may be varied and can be up to one-fourth of the length of theconnecting tube. It may be made of a rigid or a flexible impermeablematerial. The inner filter wall in FIG. 13 extends in contact with theextension 11' of the connecting tube 11. In this area the openings 23are provided both in the connecting tube and in the inner filter wall20c.

The operation of the filter tank of the invention is as follows. Withreference again to FIG. 1 it will be seen that the liquor or slurry tobe filtered enters through the inlet 2. Filter aids may be provided inthe liquor. By means of the pressure applied the liquid to be filteredis caused to penetrate the filter wall 18 of the filter elements 9. Thesolid particles to be eliminated will be deposited at the outside of thefilter wall 18 and are retained there by means of the pressure excessprevailing against the interior of the filter element 9.

A squeezing together of the filter tubing 9 is prevented by the presenceof the packing material 10. On the other hand a squeezing outwards ofthe filter material into the space receiving the clear filtrate in theconnecting tube 11 is prevented by the screen plate 19. The clearfiltrate is received in the hollow carrier member 7 and from there flowsthrough the connecting tube 8 into the annular collector tube 6. Asindicated in FIG. 3 the collector tube 6 and connecting pipe 8 may alsobe provided inside the filter tank. In this case the clear filtrate isdischarged through an outlet tube 3a.

As indicated in FIG. 4 the filtrate may also be passed out from thehollow carrier member, which in this case is in the form of an apertureddisk 16, directly into the dome space of the tank and through the outlet3a.

Upon completion of the filtration cycle the filter cake can be removedin a wet or dry process. A wet removal is possible by back washing witha rinsing liquid which may consist of water, a suitable solvent or evenclear filtrate. It is thus possible in a short time to remove thefiltrate and at the same time to accomplish a cleansing of the filterelement.

It is, however, also possible to employ gas in countercurrent to thedirection of filtration in order to remove the filter cake. The dryingof the filter cake can be effected by a gas or steam current in thedirection of the filtration.

The loosening of the filter cake can also be effected by vibration or byimpulses of compressed air.

For the drying step a filter element as seen in FIG. 9 is useful. Theremoval of the slurry as well as of the dry filter residues in all casesis effected through the opening 13 shown in FIG. 1.

In order to remove residues which have a strong adhesion it is advisableto use a rinsing liquid which can be introduced as shown in FIGS. 6 and7 by means of a pump (not shown) and the inlet 35, connecting tube 34and main distributing tube 32. The rinsing liquid is thus passed intothe individual spray tubes 30. The rinsing liquid under pressure is thensprayed through the bores or nozzles 31 onto the outer surface of thefilter tube 9. In this manner even very sticky filter residues can beremoved completely.

In order to lift an entire row of filter elements, for instace forcontrol purposes or regeneration purposes, the fastening by means of theflanges 15 and 24 in FIGS. 1 and 2 is released. This permits lifting thelid 5 and a desired row of filter elements 9 can then be removed merelyby releasing the flange 26 at the hollow carrier member 7 and the flange27 at the connecting tube 8. An entire row of filter elements can thenbe pulled out and checked or exchanged. Instead of the flanges 26, 27 itis also possible to use clutch-connections. In order to check eachspecific filter segment inspection glasses or specimen valves may beprovided in the connecting tubes outside the filter tank proper. Thepacking material for the filter elements may be either a homogenous orheterogenous material. It may consist of different materials of widelyvaried shapes.

The main use of the filter tanks and process of the invention is thefiltration of liquids. A particular advantage of the filter elements ofthe invention is their connection to the filter tank which permits themovably disposed filter tube-like filter element to be removed and alsopermits an easy removal of the filter cake.

The backwashing of the tank for removal of the filter cake can beeffected with relatively small amounts of solvents by spraying thesolvents into the tank or by a finely distributed condensate whereby thesoluble components can be dissolved out of the filter cake. In case ofexpensive solvents this is frequently of great economic importance.

A special use of the invention are catalytic reactions and decoloringprocesses for solutions.

Enzymes fixed on a carrier material, that is biocatalysts may also beused as packing material. By an approximately even thickness of thecatalyst layer and of the fixed enzymes, equal reaction times and thusequal conversion products may be obtained.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A pressure filter for media to befiltered comprisinga filter tank, optionally including an air passage;an inlet to said tank for introducing said medium under pressure; ahollow carrier member removably supported in said filter tank; aplurality of hollow elongated flexible filter members supported in rowsby said carrier member; an outer filter wall provided on said flexiblefilter elements adapted to hold back the matter to be filtered out; aninner space provided in said flexible filter member adapted to receivethe filtrate penetrating through said outer wall, said inner spacecommunicating with the interior of said hollow carrier member; meansoperative to fill said inner space of said flexible filter member and tosupport said flexible filter member during introduction of said mediumunder pressure, said means comprising packing material; discharge meansconnected to said carrier member for receiving said filtrate; an outletin said filter tank for discharging said filter residue; and means foropening and closing said filter tank, whereby after opening of the tankall or groups of said filter elements may be removed together forcleaning or replacement by means of removal of said carrier member. 2.The pressure filter of claim 1 wherein the packing material additionallycomprises a catalyst for reactions of said filtrate.
 3. The pressurefilter of claim 1 wherein said discharge means include a collector tubedisposed inside said filter tank and a discharge outlet in the wall ofsaid filter tank, said outlet communicating with said collector tube. 4.The pressure filter of claim 1 wherein said carrier member is in theform of a disk separating said filter member into an upper and lowerportion and wherein a plurality of cross channels are provided in saidcarrier member communicating with said interior space of said filterelements permitting the filtrate to pass directly into the top portionof said filter tank, the discharge means provided in said top portion ofthe tank and the outlet for the residue provided in the lower portion ofsaid tank and wherein an air passage is provided in said top portion ofthe tank.
 5. The pressure filter of claim 1 wherein said discharge meansinclude a collector tube provided outside said filter tank, a connectingtube between said collector tube and said carrier member, saidconnecting tube extending through the wall of said filter tank, thedischarge means provided at the outer end of said collecting tube. 6.The pressure filter of claim 5 which includes an abutment for looselysupporting said hollow carrier member at one end in said filter tank andincludes cooperating releasably connected flanges on the other end ofsaid carrier member and the inner end of said connecting tube.
 7. Thepressure filter of claim 1 which includes a plurality of spray pipes forpassing a rinsing fluid against the outer wall of said filter elementsand a distribution tube inside said filter tank and inlet openings inthe wall of the tank leading to said distribution tube, saiddistribution tube supporting said spray pipes and receiving the rinsingfluid passed through said inlet opening and adapted to pass the rinsingfluid to the spray pipes, said pressure filter including a dischargeopening in the filter tank for said hollow holding member.
 8. Thepressure filter of claim 1 which includes baffle means in said filtertank for directing the flow of the medium received from said inlet. 9.The pressure filter of claim 1 which includes a connecting piece forconnecting each filter element to said carrier member, said outer wallof the filter element being of a flexible material and lapping at leastpart of said connecting piece, fastening means for securing the filterelement to said connecting piece and a screen member covering the openend of said inner space so as to permit the filtrate to enter theconnecting piece and to prevent the packing material from penetratinginto said connecting piece.
 10. The pressure filter of claim 9 whereineach filter element comprises two perforated opposite wall members, theouter filter wall having a relatively close-meshed and the inner wallhaving a relatively wide-meshed structure and including openings in saidconnecting piece in the inner wall while the outer wall is continuous inthe area of said openings.
 11. The pressure filter of claim 10 whereinsaid packing material is disposed between said two walls and said innerspace is formed inside the inner wall member.
 12. The pressure filter ofclaim 10 wherein said packing material is disposed in said inner spaceformed inside the inner wall member.
 13. The pressure filter of claim 10wherein the inner wall member consists of an inner rigid tube andwherein said packing material is disposed between said two wall membersand said screen member being provided at the lower end of said rigidtube.
 14. The pressure filter of claim 10 wherein at least one of thetwo wall members of the filter element are composed of a synthetictextile material.
 15. The pressure filter of claim 10 wherein at leastone of the two wall members of the filter element is composed of anatural textile material.
 16. The pressure filter of claim 10 wherein atleast one of the two wall members of the filter element is composed of apermeable metal.
 17. The pressure filter of claim 1 wherein the packingmaterial is arranged in columns and is composed of perforated bodies ofgenerally regular shape.
 18. The pressure filter of claim 1 wherein thepacking material is composed of bodies having a specific weight below 1.